Pyrite: physical and chemical textures

Pyrite may crystallize initially in forms as diverse as framboids or cubes depending upon the temperatures and pressures. Fluid-rich diagenesis or low-grade metamorphism clearly results in thorough recrystallization and the common formation of cubes. Once these have formed, the pyrite becomes much more refractory and retains many characteristics even in deposits which have undergone penetrative deformation. This is in strong contrast to the behavior of most of the accompanying sulfides, which often undergo ductile deformation, solid state or chemical remobilization, and annealing. Pyrite deforms sparingly until there is brittle failure; however, there may be significant pyrite corrosion and regrowth during metamorphism as the result of sulfur exchange with other minerals, especially pyrrhotite. Pyrite fabrics may also be significantly modified by pressure solution or Coble creep. Optical microscopic examination and electron microprobe chemical mapping of pyrites from a variety of mineral deposits, including several high-grade metamorphic ones, reveals that the pyrites frequently contain both physical and chemical textures that may be interpreted in terms of the depositional and the post-depositional history of the deposits. Inclusions of sulfides or other minerals reveal information on the timing of the crystallization or recrystallization of the pyrite; chemical mapping of elements such as Ni, Co, and As reveals information on the relative time of transport of these elements in the ore fluids. Received: 19 March 1997 / Accepted: 14 May 1998